Delivering pressurized gas can be facilitated by first pumping or pressurizing it in a fluid phase when the substance is denser than it is in the gaseous phase. Of course, when an end user requires a gas, such a method requires an additional processing step to convert the pressurized fluid to a gas. For example, after a liquefied gas is pressurized, a heater may be employed to warm or boil the pressurized fluid to convert it into a gas. However, many applications, including lower pressure systems, do not warrant the additional equipment and processing steps required to utilize the above process, rendering this method impractical in these situations.
Frequently, where gas delivery systems experience sudden demands that cannot be met by the pump alone, an accumulator is included in the delivery system. Generally, conventional delivery systems include an accumulator preceding and often adjacent to the point of delivery allowing for an immediate supply of pressurized gas. A significant restraint on accumulators, however, is the fact that they, as storage vessels, require space. In many applications sufficient space for a conventional accumulator is not available or is impractical near the delivery point. By way of example, end users of high pressure gaseous fuels or combustion catalysts such as stand alone generators or natural gas powered vehicles typically use a plurality of fuel injection valves and thus have a plurality of delivery points for injecting fuel into an engine. Space for a conventional accumulator is typically not available next to each injection valve. In any event, space is limited in and around these engines in many cases especially where such space must be, in effect, transported along with a vehicle reducing room for storage or other uses. Examples of such fuels or combustions catalyst include methane, propane, ethane and derivatives of these hydrocarbons, as well as hydrogen and oxygen
For the purposes of this application it will be understood that any references to fluids include liquids as well as liquids pressurized above the supercritical point of the gas of interest. Similarly, any references to gases include gases pressurized above the supercritical point of those gases. More generally, if the desired substance to be delivered is to be delivered at a pressure placing it above the supercritical point of the substance, then that substance generally will also be included in any reference to a gas where corresponding fluid is, at some point in the gas delivery system, at a lower temperature and pressure prior to being delivered.